From time to time I have been tasked with drawing electrical wiring or flexible tubing routes that end up needing 3D sketched splines drawn in. Using SOLIDWORKS Premium with the routing add-in and the “auto route” feature is the easiest way to do this task But that isn’t always an option. If you have attempted to sketch a spline through a 3D sketch, you may have seen it can be trickier than you first thought. I have developed some best practices that I will outline in this article with screenshots for clarity.

Ribbon Cable Example

I will be drawing a ribbon cable in the following examples and showing some different methods I use to help control what happens. In this example we see there are electrodes on a model of a human torso that will need to all get wired together into the ribbon cable coming out of a side mounted unit

Additional Construction Sketches

Adding additional sketches to parts that will be used during this process is a good technique to help when in the 3D sketch for the wire spline. You can lock to circular edge geometry during the sketch, but typically I find having some sort of construction sketch helps ensure this process goes smoothly. Add the components to the desired assembly and fix their positions to make things easier. See ribbon cable initial stub part and sensor part with hidden sketches shown below in Figure 2.

Straighten the Initial Spline

Initially, I will edit a configuration of the ribbon cable stub part called Pos.1 in case this type of cable is reused elsewhere with different layouts. This will be done from a top-down assembly modeling approach. The first step is to start a 3D sketch. Then, using the spline tool, draw a straight spline by directly clicking between the points you wish to connect and hit ‘ESC’ to exit the command. The spline will initially just look like a line from point to point. Don’t worry, we will add the curvature in soon. (See figure 3)

Manipulate Initial Spline

Go to a view that is normal to one of the default planes that is best for you. In this view we will right click on the straight spline and “insert a spline point”.  After clicking the point down on the spline, we can click and drag (while holding “CTRL” to avoid making references to background geometry) and give our spline some curvature. After moving the spline point  from a normal view, draw some straight line segments at both ends. Setting the spline tangent to these lines locked to our part geometry will finish this spline off most of the way and typically make it look like a natural curve. One spline point can be enough for many types of simple routes, make use of the spline control handles for fine adjustment. (See series of images in figure 4)

Finishing the Feature

To finish the feature we will be using a sweep that uses a circular profile, so no need for a profile sketch. I will leave merge result checked so that it gets merged with the initial cable stub I created for the part. (See Figure 5).

Repeat as Necessary

If you need other separate wires, repeat this step between the different components to create part files in the assembly for each wire. If the wires are from a ribbon cable like in this example, or part of a wiring harness, you can draw them all in the same part file. Stay tuned for a video how to on this same topic for more information!